A plastic product designed with metallic style is used as the substitute of an article such as a car grill with chromed appearance and widely used, mainly in the automobile industry from the viewpoint of the superiority including the flexible shape, the strong corrosion resistance, lightweight, or the low price compared with metal. As a process of providing metallic luster to the surface of such a resin-molded article, particularly a molded article with a three-dimensional curve or shape, plating or painting is conducted after molding. This process requires environmental measures to wastewater, solvent vapor, and the like and suffers from height cost and the like.
In recent years, a metallic luster sheet has been used to make a molded product with a metallic luster surface by insert molding (for example, Patent documents 1 and 2).
However, in such a resin-molded article with a metallic luster surface, even a negligible damage decreases the gloss and causes whitening.
On the other hand, a decorative molded article decorated by laminating a decorative sheet on the surface is used in various applications such as automotive interior parts. The method of forming such a decorative molded article includes insert molding in which a decorative sheet is previously three-dimensionally formed with a vacuum forming mold, and then the molded sheet is inserted in an injection mold and fluidized resin is injected in the injection mold to integrate this resin with the molded sheet; and simultaneous injection-molding and decorating in which a decorative sheet inserted in a mold is integrated with a melted resin injected in the cavity during injection molding to decorate the surface of the resin-molded article (for example, Patent document 3).
The above-mentioned decorative molded article is provided with a surface protection layer in order to improve the damage resistance on the surface. However, the above-mentioned method of forming such a decorative resin-molded article has a problem in the process of previously three-dimensionally forming a decorative sheet with a vacuum forming mold in insert molding and in the process of drawing and firmly attaching a decorative sheet along the inner periphery of the cavity during preforming or during injecting a melted resin in simultaneous injection-molding and decorating. Specifically, the decorative sheet is drawn more than minimum requirement to fit the shape of the mold due to the effect of vacuum or compressed air or due to the tension or the like generated by the pressure and the shear stress of the melted resin, resulting in a crack generated on the surface protection layer on the curved surface of a molded article.
To approach the above-mentioned problems, an ionizing radiation curable resin such as an ultraviolet curable resin has been used as the surface protection layer for increasing the cross-link density of the resin forming the surface protection layer of a decorative sheet so as to attempt to improve the abrasion resistance and the damage resistance of the surface of a decorative molded article. However, the problem of a crack generated on the curved surface of a molded article during the forming still exists.
Alternatively, an ionizing radiation curable resin such as an ultraviolet curable resin used as the surface protection layer has been attempted to be half-cured at the stage of the formation of a decorative sheet and then fully cured after integrated with the decorative sheet (see Patent document 4). However, problems are created, in which the surface protection layer containing an uncured resin component is easily damaged and hardly handled and in which the mold is contaminated due to the uncured resin component adhering to the mold. To solve these problems, a protection film may be provided on a half-cured surface protection layer. However, this complicates the manufacturing process and increases the cost.
Therefore, the surface protection layer with damage resistance as well as three-dimensional moldability is desired.
A resin composition containing a polycarbonate (meth)acrylate is known (for example, Patent documents 5 and 6), and a resin composition containing a small amount of yellowing polycarbonate urethane acrylate oligomer is used for the inner colored sheet on the back side of a transparent sheet provided on the surface of a decorative sheet for insert molding (Patent document 7). However, no polycarbonate (meth)acrylates were used for the surface protection layer of a decorative sheet.
An acrylic silicone resin has the structure in which the acrylic polymer chain is strongly cross-linked by a siloxane bond, providing excellent weatherability, heat resistance, chemical resistance, and water resistance so as to be widely used in exterior paint. However, if an acrylic silicone resin is used as the surface protection layer in order to improve the damage resistance on the surface of a resin-molded article, the formed film becomes hard and fragile, possibly causing a crack. To prevent a crack from being generated, a curing process such as ultraviolet curing is applied to a sheet for insert molding after vacuum forming or to a resin molded article after injection molding when an acrylic silicone resin is used as the surface protection layer (for example, see Patent documents 8).
However, the curing process applied to a three-dimensionally molded article is complicated with poor economical efficiency, hardly providing uniform curing.
Therefore, the surface protection layer, which has three-dimensional moldability as well as damage resistance while maintaining the excellent chemical resistance of the acrylic silicone resin, is desired.